1. Field of the Invention:
The present invention relates to portable radio devices such as cellular telephones and a manufacturing method of a body that is applied to portable radio devices.
2. Background Art:
Among related art antennas that are used in portable radio devices as typified by cellular telephones are antennas that are provided such that they can be pulled out from the top portion of a body. Since antennas of this kind are accommodated in a body in an unused state and can be pulled out of the body when used, it can be said that their structures are superior in portability and provide superior antenna characteristics.
FIG. 7 shows an attachment structure of an antenna that is provided in a related art cellular telephone. An antenna 100 is attached to an antenna holder 101. The antenna holder 101 can be screwed into a nut 103 that is fixed to a body 102. The antenna 100 is attached to the body 102 in such a manner that the antenna holder 101 is screwed into the nut 103 in a state that the antenna 100 is attached to the antenna holder 101.
Incidentally, antennas used in cellular telephones are usually required to have a superior circular polarization characteristic. To satisfy this requirement, the present assignee has proposed an antenna which can provide a superior circular polarization characteristic. Specifically, this antenna has a first cylindrical antenna that is fixed to the top portion of the body of a cellular telephone and a second cylindrical antenna that can be pulled out so as to be placed in the internal space of the first antenna in a non-contact state. A plurality of dipole array antenna elements are formed on the circumferential surface of the first antenna. A plurality of helical antenna elements are formed on the circumferential surface of the second antenna. When pulled out of the first antenna, the second antenna is erected so as to come close to the top portion of the first antenna. In this state, the antenna elements of the first antenna and those of the second antenna are brought into capacitive coupling, whereby a superior circular polarization characteristic can be obtained.
As for the antenna having the above structure, in fixing the first antenna to the body, it is conceivable to attach the first antenna to an antenna holder and then screwing the antenna holder into a nut in the same manner as described above. However, in this case, it is necessary to bury the nut in the top portion of the body and then screw the antenna holder that is fitted with the first antenna into the nut. Therefore, there is fear of a problem that in manufacturing a body with an antenna the manufacturing work is very cumbersome and the manufacture takes a long time.
In view of the above, an object of the present invention is to provide a portable radio device which has a movable second antenna that is so provided that it can be pulled out so as not to contact the inner circumferential surface of a fixed first antenna, and which can simplify a manufacturing process.
Another object of the invention is to provide a manufacturing method of a body which can simplify a manufacturing process of a portable radio device body in which an antenna formed with antenna elements is attached to the inner circumferential surface of an antenna attachment portion that projects outward from a body main part.
To attain the above objects, the invention provides a portable radio device comprising a body incorporating a transmission/reception circuit for radio communication and having a cylindrical antenna attachment portion that projects outward; and an antenna device having a first antenna that is attached to the antenna attachment portion and a second antenna that is provided movably and is to be electrically coupled with the first antenna, wherein the first antenna has first antenna elements that are formed on a circumferential surface and electrically connected to the transmission/reception circuit, and is integrally molded with the antenna attachment portion such that the first antenna elements come into close contact with an inner circumferential surface of the antenna attachment portion.
In the invention, the first antenna is attached to the body in such a manner that the first antenna is integrally molded with the antenna attachment portion. Therefore, unlike the related art case, manufacture of this portable radio device does not require work of burying a nut in the body and screwing an antenna holder into the nut. Therefore, the manufacturing process of this portable radio device can be simplified and hence its manufacturing efficiency can be increased.
Since the antenna element surface of the first antenna is in close contact with the inner circumferential surface of the antenna attachment portion. Therefore, for example, even if the antenna element surface is formed on the outer circumferential surface of the first antenna, the antenna element surface can be protected properly. This advantage is particularly effective in case where the first antenna elements are formed by plating a thin conductive metal that is prone to be damaged.
No accompanied parts such as a nut for attaching the first antenna to the body are necessary at all. Therefore, no space other than the attachment space of the first antenna is necessary. This makes it possible to miniaturize portable radio devices as typified by cellular telephones. Therefore, the invention makes it possible to provide portable radio devices that are superior in portability and have improved user interfaces.
Further, since the first antenna is integrally molded with the body main part and the antenna attachment portion, the relative positional error between the first antenna and a circuit board can be made within a prescribed range. Therefore, the first antenna elements and the transmission/reception circuit can be connected to each other at correct positions.
According to another aspect of the invention, there is provided a manufacturing method of a portable radio device body that has a cylindrical antenna attachment portion projecting outward from a body main part and in which a cylindrical antenna formed with antenna elements is attached to an inner circumferential surface of the antenna attachment portion, comprising the steps of positioning the antenna in a die that is formed with a main part cavity having a shape corresponding to the body main part and an antenna cavity having a shape corresponding to the antenna attachment portion such that the antenna elements are faced at an inner circumferential surface of the antenna cavity; and forming the body main part and the antenna attachment portion and simultaneously integrally molding them each other such that the antenna elements of the antenna come into close contact with the inner circumferential surface of the antenna attachment portion by injecting a resin into the main part cavity and the antenna cavity.
In the invention, in producing the portable radio device body to which the antenna is to be attached, the body is molded with a resin and, at the same time, the antenna is integrally attached to the inner circumferential surface of the antenna attachment portion. Therefore, unlike the related art case, work of burying a nut in the body and screwing an antenna holder into the nut is not necessary. Therefore, the manufacturing process of this portable radio device body can be simplified and hence, its manufacturing efficiency can be increased. Further, since the body and the antenna can be produced at the same time, it is not necessary to manage the number of bodies and the number of antennas separately. This decreases the burden on operators.